2070Exam3AProbF11_Soln - Physics 2070 Exam 3ABlue Fall 2011...

Physics 2070 Exam 3A—Blue Fall 2011 Problems. Be organized, show all work, and circle your answer. 1. (6 points) Answer the following questions about blocks 1, 2, 3, and 4, with m 1 <m 2 <m 3 <m 4 , but with the same dimensions (size and shape). a. Suppose blocks 1 and 2 are held below the surface of a container of water by ropes, as shown. i. What is the direction of the force on block 1 by the water? Explain. The water exerts a net upward force on the block. This is the buoyant force and is caused by the difference in pressure exerted by the water on the top and bottom surfaces of the block. ii. Is the force on block 1 by the water greater than, less than, or equal to the force on block 2 by the water? Explain. The forces are equal. The blocks have the same volume and the buoyant force only depends on the volume of water displaced. iii. Will the tension in the string holding block 1 be greater than, less than, or equal to the tension in the string holding block 2? Explain. T 1 > T 2 . Block 2 has a larger weight, so the string will not have to pull as hard on block 2 to counteract the upward buoyant force exerted by the water to keep it submerged. b. Two identical beakers are initially filled with water to the same height. Block 3 is placed in one of the beakers and the water level after it sinks to the bottom is shown. Block 4 is submerged in the second beaker. In this case the water level is not shown. i.

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